The electromagnetic flow transducer is well known to those skilled in the art; for example, see my prior U.S. Pat. No. 3,759,097. The transducer itself comprises at least a magnetic field producing device and a plurality of sensing electrodes adapted to sense the voltage induced by reason of the flow of a medium in which the transducer is situated. Since the transducer is limited to measuring flow in the plane in which the sensing electrode is lying, it has been proposed in the past to use a plurality of transducers to sense flow at different depths in a medium, such as in a body of water, for example, the ocean. To perform such a function, the plurality of transducers must, of course, be supported at different depths in the medium and normally the transducers are supported from above by some apparatus mounted on or above the surface of the medium.
To provide such an arrangement a cable may be provided to support the plurality of transducers at different depths in the medium. In addition, certain types of electromagnetic transducers require plural conductors connecting the transducer to surface mounted apparatus. Such conductors may be required, for instance, to provide energizing power for the transducer and/or to conduct the signals generated by the transducer to the surface for recording and/or transmission. The conventional practice has been to provide a support cable, either separately or in conjunction with the signal or power conductors, of various lengths equal to the distance between the several transducers. This practice requires, for instance, the first or uppermost transducer to be attached to the end of an appropriate length of cable and then, in those cases in which the cable includes conductors, making appropriate conductive connections to the different transducers, for each conductor. Once such an arrangement has been fabricated, it is obviously impossible to vary the depths at which the various transducers are located without providing new lengths of cables. In addition, the separate connection required for each conductor, to each transducer, is time-consuming, subject to error and increases the possibility of failures. For example, while only six or so conductors may be necessary for each transducer, the conventional practice would require approximately 12 connections multiplied by the total number of transducers for each transducer. This can rapidly reach burdensome proportions for even only three transducers.
The prior art provides some relevant teachings, although a review of this art indicates that the difficulties in providing an electromagnetic flow transducer which can be located at any selected point on a cable, for detecting open field flows, have not been overcome. In particular, teachings such as those of Wyatt (U.S. Pat. No. 3,681,986) and Westersten (U.S. Pat. No. 3,712,133) teach providing electromagnetic flow meters for measuring flow in confined conduits, where the transducer is in the form of an annulus surrounding the conduit. Although such transducers can be placed at any location on the conduit, they are not suitable for detecting open field flow. On the other hand, reference such as Kahl (U.S. Pat. No. 3,769,928), Hickey (U.S. Pat. No. 3,927,562) and Murdock (U.S. Pat. No. 3,314,009) disclose providing transducers for measurement in open bodies, which transducers can be located at any point on a cable. However, the first two mentioned patents do not relate to electromagnetic flow transducers. The last-mentioned patent relates to detecting characteristics of sea water including flow velocity and direction. While the device disclosed may be suitable for measuring such scalar quantities such as pressure, temperature, salinity, etc., it has a significant drawback in terms of measuring vector quantities, such as flow velocity and direction. In particular, reference to that patent will illustrate that it is asymmetrical, in that the transducer, per se, (referred to as 32 in FIG. 3 for instance) is asymmetrically located with regard to the cable. Depending upon the flow direction, with respect to the transducer's location relative to the cable, the transducer may well be in the wake or shadow of the cable, and thus produce signals which are not truly representative of flow velocity and direction in undisturbed areas.
Therefore, it is one object of the present invention to provide an electromagnetic flow transducer which is adapted to be located at any point on a continuous cable. It is another object of the present invention to provide such a transducer which can be so connected at any point on a continuous cable which includes a plurality of different conductors. It is still another object of the present invention to provide an electromagnetic flow transducer of the foregoing type in which the only conductive connections that are necessary are those which are appropriate to that transducer. It is yet another object of the present invention to provide an electromagnetic flow transducer of the foregoing type which simplifies the electrical and support connections for multi-transducer apparatus.